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发表于 2005-10-3 11:31:36
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来自 美国
Re:怎么计算温度场和浓度场的耦合.请教临江仙.
I totally agree with your opinion that the second PDE is indendent of the first one. If i write codes to compute these two PDEs, my method will be the same as you present here.
But Femlab solves all the equations at the same time (unless you use the solve for function). For this problem, femlab can not know which is indendent of which.
The reasion for not using second derivative in the source term is that femlab internally only applys the "integration by part" on the divergence term, i.e. on the flux, not on the source term. If the second derivative can be used in the source term, there is no need to apply the "integration by part" on the divergence term: consequently, there will be no Finite Element Method.
using the second derivative on the source term will undermine the foundation of FEM, for more informtion, please read guide.pdf (theoretical background-deriving the weak form).
Of course, you can get solution if you use second derivative in the source term, but even if you get the soluion, what you get is not the real solution of finite element method.
----BTW---
the non-FEM solution can also be obtained in most cases when people use user-defined functions in femlab, whichi i will address if time permits in the near future.
cheers |
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